Dealing with matrix effect: should there be a cut-off limit for signal ion suppression in quantitative assay validation?

Simultaneous Determination of Urine Methotrexate, 7-Hydroxy Methotrexate, Deoxyaminopteroic Acid, and 7-Hydroxy Deoxyaminopteroic Acid by UHPLC-MS/MS in Patients Receiving High-dose Methotrexate Therapy

Nephrotoxicity, the most important toxicity in high-dose methotrexate (MTX) therapy, is partly caused by the formation of crystal deposits in the kidney due to poor water solubility of MTX and its metabolites 7-hydroxy methotrexate (7-OH MTX), deoxyaminopteroic acid (DAMPA) and 7-hydroxy deoxyaminopteroic acid (7-OH DAMPA). Plasma MTX level-guided urine alkalinization, leucovorin rescue and glucarpidase detoxification are common strategies to overcome MTX-related nephrotoxicity. However, overestimation is a problem for MTX analysis by immunoassays due to the cross-reactivity of MTX metabolites (7-OH MTX and DAMPA). An UHPLC-MS/MS method for the simultaneous determination of MTX, 7-OH MTX, DAMPA and 7-OH DAMPA in human urine was developed, validated and applied in clinical practice. Samples were treated by one-step protein precipitation and analyzed within 3 min. The calibration range was 0.02 to 4 μmol/L for MTX and DAMPA, and 0.1 to 20 μmol/L for 7-OH MTX and 7-OH DAMPA. For all analytes, the intra-day and inter-day bias and imprecision were -8.0 to 7.6 and <9.0%, the internal standard normalized recovery and matrix factor were 92.34 to 109.49 and <20.68%. The plasma MTX and 7-OH MTX levels increased with the urine drug levels, age, serum creatinine and alanine transaminase, but urine could not replace blood for MTX monitoring due to their poor correlation (R², 0.16 to 0.51). Dose-normalized urine and plasma MTX and 7-OH MTX levels were similar between different patient groups (urine pH <7 or ≥7). Due to the large inter-individual variance of the analytes levels in both plasma and urine, these findings should be treated with caution.

Sensitive and specific LC-ESI-MS/MS method for determination of ZYDPLA1, a novel long-acting dipeptidyl peptidase 4 inhibitor in rat plasma: An application for toxicokinetic study in rats

A rapid and highly specific assay was developed and validated for the estimation of ZYDPLA1 in rat plasma using liquid chromatography coupled to tandem mass spectrometry with positive electrospray ionization. Method validation comprised of parameters such as specificity, matrix effect, precision, accuracy, recovery, stability, etc. The assay procedure involved a simple protein precipitation of ZYDPLA1 and alprazolam (internal standard) from rat plasma using acetonitrile. Chromatographic separation was achieved with a gradient mobile phase comprising: (A) 0.2% ammonia in purified water; (B) 0.1% formic acid in isopropyl alcohol/methanol (1: 1 v/v); and (C) acetonitrile at a flow rate of 1 mL/min on an ACE-5, C18 (4.6 × 50 mm) column with a run time of 5.5 min. The quantitation of ZYDPLA1 was achieved by the summation of four multiple reaction mode transitions (m/z 399.7 → 383.0, 399.7 → 276.10, 399.7 → 153.20 and 399.7 → 127.20), while that of the internal standard was by a single multiple reaction mode transition (m/z 309.10 → 281.00). The lower limit of quantitation achieved was 0.01 μg/mL and the method showed linearity from 0.01 to 25 μg/mL. The intra- and inter-day precision (%CV) of the quality control samples was within 8.81% and accuracy was ±10% of nominal values. This novel method was applied for evaluation of toxicokinetics of ZYDLA1 in rats.

Bioanalysis in oncology drug discovery

Bioanalysis is an important aspect of drug discovery process regardless of the chosen therapeutic area. There is a general misconception that bioanalysis is seldom important during the drug discovery process because there is no scrutiny of the data from a regulatory perspective. However, bioanalytical data gathered during the discovery stage enable several key decision(s) inclusive of termination of the program and/or creating adequate differentiation from the lead competitive molecules. The review covers various stage gate screens and experimental designs where bioanalytical data are extensively used for making an informed decision during the process of drug discovery.